I. Field of the Invention
This invention relates in general to complex metal hydrides and their synthesis and, in particular, to an economical and highly advantageous stoichiometric process for production of alkali metal aluminum tetrahydrides.
II. Description of the Prior Art
The alkali metal aluminum hydrides have been made in the past by various techniques which have not proven to be economical for one reason or another. Various processes have been proposed for making alkali metal aluminum hydrides in both hydrocarbon and other solvents from alkali metal hydrides and from the elements. Such processes required extremely long reaction times (10-20 hours). Thus, there exists a need for a process to efficiently produce alkali metal aluminum hydrides, especially the tetrahydrides.
The tetrahydrides find use in reaction with various silicon-containing compounds to produce high purity silicon as a product of commerce primarily for semiconductor use. Of course, the alkali metal tetrahydrides have been used for other purposes as well. The worldwide production of sodium aluminum tetrahydride is quite low and I know of only one major producer.
Various metal catalysts have been used in the past for reaction promotion. These metals include titanium, scandium, and others. However, their use was suggested only for promotion of reactions to prepare organoaluminums. Many commercially available aluminums contain a trace amount of titanium, usually about 10 to 100 ppm on a weight basis. Other aluminums with high titanium (or similar metal) content are available but are not usually considered for chemical synthesis because of contamination.
In U.S. Pat. No. 4,081,524, Ashby disclosed the pressure hydrogenation of an alkali metal (sodium) with aluminum in the presence of a metal alkyl such as triethylaluminum. However, the shortest total reaction time reported for metal reactants was about 4.75 hours even at the extreme reaction conditions of 5000 psi and 160.degree. C.
Reference is made to related co-pending application Ser. No. 457,897, filed Jan. 14, 1983, in my name, and co-pending application Ser. No. 496,474 filed May 20, 1983 in the name of M. F. Gautreaux. Those two applications and this application are commonly assigned. This application is also related to my co-pening U.S. Application Ser. No. 490,791, filed May 2, 1983.